1. Technical
Field. The present invention relates to a centrifugal clutch with belt tightening spacer assembly for transmitting power equally through two belts. The assembly is particularly suited for transmitting drive forces to a rotary trowel used for finishing concrete.
2. Background Art
Centrifugally operable clutches, torque converters, and belt tightening devices are well-known in the patented prior art as evidenced by Erbach, U.S. Pat. No. 2,104,074, Wolff, U.S. Pat. No. 2,508,558 and Vaughn, et al., U.S. Pat. No. 3,269,200 and by the British Patent No. 866,550. Although most prior devices are of the single belt type, the Erbach patent discloses an automatic clutch for multiple belt drives. The Erbach clutch includes a floating annular section having V-belts on either side thereof and an axially displaceable annular section which is driven by another V-belt. Rotation of an input shaft causes weights to be displaced radially outwardly to axially displace the annular section against the floating section to take up the slack and drive the belts.
While the prior devices normally operate satisfactorily, they possess certain inherent drawbacks. The Erbach device, for example, requires that one of the belts be in constant contact with the drive mechanism, which results in uneven wear of the belts of the multibelt system. Furthermore, the Erbach clutch requires a constant speed for operation, limiting the applications and versatility of the device.
As described in U.S. Pat. No. 4,743,221, dated May 10, 1988, I recently developed an improved centrifugal clutch belt tightening assembly which provided a variable speed centrifugal clutch belt tightening assembly for transmitting power equally to a plurality of belts. The assembly includes a spindle adapted for rotation about a longitudinal axis having a cylindrical portion and an annular flange portion extending outwardly from one end of the cylindrical portion. A clutch plate is connected with the other end of the spindle cylindrical portion for rotation with the spindle about the longitudinal axis. A belt drive mechanism is mounted on the spindle between the flange portion and the clutch plate. The drive mechanism includes a clutch drum slidably connected with the cylindrical portion and rotatably driven about the longitudinal axis by the clutch plate, at least one spacer freely mounted on the cylindrical portion in spaced relation between the clutch drum and the flange portion for defining annular recesses for receiving the belts, and a plurality of weights arranged between the clutch plate and the clutch drum. As the spindle rotates, the weights move radially outwardly in response to centrifugal force and displace the clutch drum longitudinally toward the spacers and the flange portion to compress the spacers evenly against the belts, whereby the rotation of the spindle is evenly transmitted to the belts to drive the belts at equal speeds.
While the variable speed centrifugal clutch belt tightening assembly described in U.S. Pat. No. 4,743,221 works well, the freely rotating spacer subassembly includes bearing balls retained within spacer grooves notched in the spindle and held in place between the spindle and the spacer by an annular bearing retainer ring attached to the spacer, or a roller bearing assembly, which allows the spacer to freely rotate around the spindle and also to provide for limited travel along the length of the spindle during clutch operation. The fabrication of this spacer subassembly with bearing balls or a roller bearing requires significant additional machining steps during manufacture, and is a relatively difficult subassembly to assemble.